1. Field of the Invention
The present invention relates to solid-state laser materials, and specifically to noncritical phase matching laser materials capable of non-linear harmonic conversion of a specific wavelength.
2. State of Technology
Ytterbium doped laser hosts emit in the wavelength range between 970 nm and 1047 nm. Some examples of these crystals are Ytterbium doped strontium fluoro-apatite (i.e., Yb:SFAP), Ytterbium doped yttrium aluminum garnet (Yb:YAG), Ytterbium aluminum garnet (YbAG), Yb doped glass (Yb:glass), Yb doped potassium gadolinium tungstate (Yb:KGd(WO4)2), and Ytterbium doped fused silica (Yb:SiO2). Each host has specific application and utility. Collectively, these lasers emit in the range of 970-1045 nm. For example, Yb:SFAP emits at several specific wavelengths, such as 1047 and 985 nm. As another example, Yb:YAG has a tunable laser emission between 1020 and 1045 nm, with a peak emission occurring at 1030 nm.
Frequency conversion of such lasers discussed above has been found to be useful for many applications. For example, frequency doubling of the 1029-nm emission of Yb:YAG leads to laser light at the wavelength of 514.5 nm. This specific wavelength is emitted by the Argon-ion laser and is a wavelength that has many beneficial and useful applications. For example, the 514.5-nm wavelength is useful in the biotechnology field for cell sorting of biological compounds. By utilizing frequency conversion, a solid-state frequency converted laser has the potential to replace the Ar-ion gas laser for this specific wavelength.
Background information on improved frequency mixing crystals for harmonic generation of laser beams is contained in U.S. Pat. No. 5,123,022 entitled “Frequency Mixing Crystal,” to Ebbers et al., patented Jun. 16, 1992 including the following: “The improvement of said means of harmonic generation comprising a crystal having the chemical formula X2Y(NO3)5.2nZ2O wherein X is selected from the group consisting of Li, Na, K, Rb, Cs, and Tl; Y is selected from the group consisting of Sc, Y, La, Ce, Nd, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, and In; Z is selected from the group consisting of H and D; and n ranges from 0 to 4.”
Background information on frequency mixing crystals by congruently melted compositions including a lanthanide is contained in international application No. WO 96/26464 entitled “Non-linear Crystals And Uses Thereof,” to Gerard et al., patented Feb. 16, 1996, including the following: “The crystals are prepared by crystallizing a congruent melting composition of general formula: M2LnO(BO3)3, wherein M is Ca or Ca partially substituted by Sr or Ba, and Ln is a lanthanide from the group which includes Y, Gd, La and Lu. Said crystals are useful as frequency doublers and mixers, as an optical parametric oscillator or, when partially substituted by Nd3+, as a frequency doubling crystal.
Accordingly, a need exists to improve solid-state frequency materials for specific wavelengths. An ideal crystal is not difficult to grow, has a high nonlinear optical coefficient, has a high optical damage threshold, and birefringence and contains dispersion properties that allow for noncritical phasematching at specific wavelengths. The present invention involves such a crystal.